1. Field of the Invention
The present invention relates to an autotensioner for imparting a suitable tension to a belt and attenuating the vibration generated at the belt.
2. Description of the Related Art
An autotensioner is provided with a pulley attached to the end of a swing member swingably supported by a support shaft, so that a suitable tension imparted to a belt, which is in contact with a pulley, due to a change of the relative position of the pulley in association with swing of the swing member. The rotating shaft of the pulley is parallel to and away from the support shaft by a predetermined distance. While the distance between the two shafts is reduced because of the demand for reduction of the size of the autotensioner, the pulley or belt has to be provided at a position different in the axial direction from the swing member so that it can rotate without interfering with the swing member.
Since the pulley is pushed in one direction when the belt is tensioned, a moment load making the swing member tilt about the support shaft acts on the swing member. The further the position in the axial direction away from the swing member, the larger the moment load, so a problem arises where the swing member is easily tilted.
Therefore, an object of the present invention is to provide an autotensioner in which tilt of the swing member is reduced and the assembly is made as small as possible.
According to the present invention, there is provided an autotensioner comprising a base, a support shaft fixed to the base, a swing member, a pulley and a damping member.
The swing member has a cup having a bottom and opening toward the base, a bearing extending from the bottom toward the base and supported by the support shaft, and an arm extending from an outer circumferential surface of the cup. The swing member can swing about a rotational axis of the support shaft. The pulley is attached to an end of the arm. The damping member is fixed to the base and provided at a position close to the base in comparison with the bearing. The damping member frictionally slides over the approximately entire circumference with respect to an inner circumferential surface of the cup, and supports the swing member.
The autotensioner may further comprise a ring-shaped spring. In this case, the damping member is provided with a tubular portion having the rotational axis as the axial center and is biased by the ring-shaped spring provided inside the tubular portion by a substantially uniform force in the circumferential direction toward the inner circumferential surface of the cup.
Preferably, the autotensioner further comprises a torsion coil spring wound spirally around the support shaft. The torsion coil has two ends engaged with a bottom of the cup and the base. The base side of the torsion coil spring is formed into a pigtail end shape so as to avoid interference with the damping member and the ring-shaped spring. Due to this, it is possible to make efficient use of the space in the cup and reduce the size of the autotensioner.
The inner circumferential surface of the cup may be provided with a step such that the inner diameter of a part of the bottom side of the inner circumferential surface becomes smaller than the inner diameter of the other part of the inner circumferential surface. The damping member is provided inside the other part, so that the damping member is positioned in the axial direction. Preferably, a part of the damping member is inserted to the other part of the inner circumferential surface.
The damping member may have an outer circumferential surface provided with a flange, which is provided between the opening of the cup and the base and is in close contact with the cup and the base. Due to this, interference between the cup and the base and entry of dust and water, etc. into the cup is prevented. In this construction, the outer diameter of the flange may coincide with the outer diameter of the cup. Further, the base may be provided with a first circular groove, which is provided with a second circular groove formed concentrically inside the first circular groove. The outer circumferential surface of the damping member is in close contact with a side surface of the second circular groove, an end surface of the base side of the damping member is in close contact with the bottom of the second circular groove.